Rare-earth metal vanadates catalysts for NOx reduction at low temperatures

ABSTRACT

Provided are catalysts for reduction of nitrogen oxides including an active site including lanthanum vanadate represented by at least one of Formula 1 and Formula 2 and a support carrying the active site.
 
LaVO 4  (wherein LaVO 4  is polymorphous and has a tetragonal or monoclinic crystal structure)  Formula 1
 
LaV 3 O 9  (wherein LaV 3 O 9  has a monoclinic crystal structure)  Formula 2.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2020-0050936, filed on Apr. 27, 2020, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein in itsentirety by reference.

BACKGROUND 1. Field

The present invention relates to a rear-earth metal vanadate catalystfor reduction of nitrogen oxides (NO_(X)), and more particularly, to aheterogeneous catalyst for NO_(X) reduction including a lanthanumvanadate as an active site in a support and a method of manufacturingthe same.

2. Description of the Related Art

Recently, selective catalytic reduction of NO_(X) (SCR) for stably, withhigh efficiency, converting nitrogen oxides (NO_(X)), one of the maincauses of secondary fine dusts, with ammonia (NH₃) proceeds according toReaction Schemes 1 and 2.4NO+4NH₃+O₂→4N₂+6H₂O  (1)2NO₂+4NH₃+O₂→3N₂+6H₂O  (2)

Enhancement of performance, stability, and persistence of theabove-described SCR process is possible by improving surfacecharacteristics of a commercially available catalyst applied to the SCRprocess. For example, representative examples of the commerciallyavailable catalyst applied to SCR processes of power plants, sinteringfurnaces, low-speed and high-speed ships, and cement factories arevanadium oxide-WO₃/TiO₂ (where a vanadium oxide (V oxide) includes atleast one species selected from V₂O₃, VO₂, and V₂O₅). One of the methodsfor enhancing surface characteristics of the commercially availablecatalyst may be structural modification of the vanadium oxide (V oxide)applied as an active site of the catalyst. Specifically, metal vanadatesformed by chemical fusion of a vanadium oxide and either of a transitionmetal TM oxide or a rare-earth metal RM oxide may be used as activesites of SCR reaction. More specifically, metal vanadates, as compositeoxides of vanadium and either of transition metal or rear-earth metal,may solve at least one of the following problems of or requirements forvanadium oxide active sites included in the commercially availablecatalyst: (1) congregation phenomenon of catalytic active sitesoccurring during SCR reaction due to low melting point, (2) relativelylow redox cycling traits, (3) relatively small numbers of Brönsted acidsites or Lewis acid sites, (4) decreased SCR reaction efficiency perunit hour due to weak interaction between NH₃/NO_(X) and acid sites orstrong interaction between H₂O and acid sites, (5) absence of rapid SCRreaction at low temperature (Reaction Scheme 3), (6) insufficientdurability against poisoning by SO₂ contained in exhaust gas on thesurface of the catalyst, (7) insufficient durability against poisoningby ammonium sulfate ((NR₄)₂SO₄), AS) and ammonium bisulfate ((NH₄)HSO₄),ABS) generated during SCR reaction based on a series of chemicalreactions according to Reaction Schemes 4 to 6 on the surface of thecatalyst, (8) insufficient durability against poisoning by analkali-metal-based compound contained in exhaust gas on the surface ofthe catalyst, and 9) insufficient durability against hydrothermal agingdue to structural instability of the vanadium oxide active site or thesupport.

For example, in the case of the transition metal vanadates (TM)V₂O₆(where TM=Mn, Co, Ni, or Cu), Cu₃V₂O₈, and Fe₂V₄O₁₃, at least one of theproblems or requirements described above in (1) to (7) may be improvedcompared to the commercial catalyst, and in the case of the rear-earthmetal vanadates CeVO₄, ErVO₄, and TbVO₄, the problems described above in(8) and (9) may be improved compared to the commercial catalyst.NO+NO₂+2NH₃→2N₂+3H₂O  (3)SO₂+½O₂→SO₃  (4)SO₃+2NH₃+H₂O→(NH₄)₂SO₄  (5)SO₃+NH₃+H₂O→(NH₄)HSO₄  (6)

However, despite the advantages of the above-described rear-earth metalvanadates as active sites of the SCR catalyst, a catalytic crystal phasecharacterized only by (RM)VO₄ (where RM is a rear-earth metal, RM=Ce,Er, Tb, or Yb) has only been reported to data.

SUMMARY

The present invention has been proposed to solve various problems of thecommercial catalysts including the above problems, and an object of thepresent invention is to provide a rear-earth metal vanadate as acatalytic crystal phase of SCR reaction. Specifically, provided is aheterogeneous catalyst including at least one type of lanthanum vanadatecrystal phases as active sites of SCR reaction, having superiorcatalytic characteristics to commercial catalyst, and manufactured withlower costs and a method of manufacturing the same. The presentinvention also provides a heterogeneous catalyst having improves acidcharacter, redox cycling feature, and durability against poisoningsubstances (H₂O, SO₂, AS/ABS, and alkali-metal) and hydrothermal agingby functionalizing (sulfating) the surface of the catalyst with SO_(Y)²⁻ (where Y is 3 or 4) or including an oxide of a Group 15 or 16 elementas a promotor, and a method of manufacturing the catalyst. However,these problems are exemplary, and the scope of the present invention isnot limited thereby.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented embodiments.

According to an aspect of the present invention, provided is a catalystfor reduction of nitrogen oxides including: an active site includinglanthanum vanadate represented by Formula 1 or Formula 2; and a supportcarrying the active site,LaVO₄ (wherein LaVO₄ is polymorphous and has a tetragonal or monocliniccrystal structure)  Formula 1LaV₃O₉ (wherein LaV₃O₉ has a monoclinic crystal structure.  Formula 2

According to another aspect of the present invention, provided is acatalyst for reduction of nitrogen oxides including: a first active siteincluding a vanadate represented by Formula 1; a second active siteincluding a vanadate represented by Formula 2; and a support carryingboth the first active site and the second active site.

According to an embodiment of the present invention, the support mayfurther include an oxide of a Group 15 or 16 element as a promotor.

According to an embodiment of the present invention, the Group 15 or 16element may be one element selected from the group consisting ofnitrogen (N), phosphorus (P), sulfur (S), arsenic (As), selenium (Se),antimony (Sb), tellurium (Te), bismuth (Bi), polonium (Po), moscovium(Mc), and livermorium (Lv), or any combination thereof.

According to an embodiment of the present invention, at least oneportion of the surface of the catalyst may be sulfated.

According to an embodiment of the present invention, the support mayinclude one of carbon (C), Al₂O₃, MgO, ZrO₂, CeO₂, TiO₂, and SiO₂.

According to an embodiment of the present invention, the amount of thelanthanum vanadate represented by Formula 1 or the lanthanum vanadaterepresented by Formula 2 may be in the range of 10⁻⁴ parts by weight to50 parts by weight based on 100 parts by weight of the support.

According to an embodiment of the present invention, the support mayhave a porous structure.

According to another aspect of the present invention, provided is amethod of manufacturing a catalyst for reduction of nitrogen oxidesincluding: mixing a vanadium precursor solution with a lanthanumprecursor solution; adding a material constituting a support to themixed solution; and obtaining solids from the mixed solution, andcalcining the solids to prepare a catalyst including a support carryinga lanthanum vanadate represented by Formula 1 or 2 as an active site orboth a lanthanum vanadate represented by Formula 1 as a first activesite and a lanthanum vanadate represented by Formula 2 as a secondactive site,LaVO₄ (wherein LaVO₄ is polymorphous and has a tetragonal or monocliniccrystal structure)  Formula 1LaV₃O₉ (wherein LaV₃O₉ has a monoclinic crystal structure).  Formula 2

According to an embodiment of the present invention, the vanadiumprecursor solution may include a solution in which at least one ofNH₄VO₃, NaVO₃, VCl₂, VCl₃, VBr₃, VCl₃·3C₄H₈O, VO(C₅H₇O₂)₂, VO(OC₂H₅)₃,VC₁₀H₁₀Cl₂, VC₁₈H₁₄I, VOCl₃, VOF₃, VO(OCH(CH₃)₂)₃, V(C₅H₇O₂)₃, VOSO₄,and V(C₅H₅)₂ is dissolved.

According to an embodiment of the present invention, the lanthanumprecursor solution may include a solution in which at least one of LaF₃,LaB₆, LaCI₃, La(CH₃CO₂)₃, Lal₃, La₂(C₂O₄)₃, La(CF₃SO₃)₃, La(NO₃)₃,La(C₉H₂₁O₃), La(C₅H₇O₂)₃, LaBr₃, LaPO₄, La₂(CO₃)₃, La(OH)₃, andLa₂(SO₄)₃ is dissolved.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 shows observation results of catalysts manufactured in Examples 1to 5 according to the present invention using a scanning electronmicroscope (SEM);

FIG. 2 shows observation results of the catalysts manufactured inExamples 1 to 5 according to the present invention using a highresolution transmission electron microscope (HRTEM);

FIG. 3 is a graph illustrating X-ray diffraction patterns (XRD patterns)of the catalysts manufactured in Examples 1 to 5 according to thepresent invention;

FIG. 4 is a graph illustrating selected area electron diffractionpatterns (SAED patterns) of the catalysts manufactured in Examples 1 to5 according to the present invention; and

FIGS. 5 to 10 are graphs illustrating SCR performance analysis resultsof catalysts prepared in examples according to the present invention andcomparative examples.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that show, by way of illustration, specificembodiments in which the invention may be practiced. These embodimentsare described in sufficient detail to enable those skilled in the art topractice the invention. It is to be understood that the variousembodiments of the invention, although different, are not necessarilymutually exclusive. For example, a particular feature, structure, orcharacteristic described herein, in connection with one embodiment, maybe implemented within other embodiments without departing from thespirit and scope of the invention. In addition, it is to be understoodthat the location or arrangement of individual elements within eachdisclosed embodiment may be modified without departing from the spiritand scope of the invention. The following detailed description is,therefore, not to be taken in a limiting sense, and the scope of thepresent invention is defined only by the appended claims, appropriatelyinterpreted, along with the full range of equivalents to which theclaims are entitled. In the drawings, like numerals refer to the same orsimilar functionality throughout the several views and some elements inthe drawings may be exaggerated for descriptive convenience.

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings so that theseembodiments may be readily implemented by those skilled in the art.

A catalyst for selective catalytic reduction of NO_(X) (SCR catalyst)according to an embodiment of the present invention includes an activesite from which a product is desorbed after a reactant is adsorbedthereto and reacted thereon, and a support carrying the active site.

Catalysts for NO_(X) reduction according to first and second embodimentsinclude a lanthanum vanadate having a tetragonal (t) phase or amonoclinic (m) phase represented by Formula 1 below as active sites.They are referred to as “t-LaVO₄” and “m-LaVO₄”, respectively.LaVO₄ (wherein LaVO₄ is polymorphous and has a tetragonal or monocliniccrystal structure)  Formula 1

Catalysts for NO_(X) reduction according to a third embodiment of thepresent invention include both a lanthanum vanadate having thetetragonal (t) phase or the monoclinic (m) phase represented by Formula1 and a lanthanum vanadate having the monoclinic (m) phase representedby Formula 2 as active sites. They are referred to as “t-LaVO₄/m-LaV₃O₉”or “m-LaVO₄/m-LaV₃O₉”.LaV₃O₉ (wherein LaV₃O₉ has a monoclinic crystal structure)  Formula 2

Catalysts for NO_(X) reduction according to a fourth embodiment of thepresent invention include a lanthanum vanadate having the monoclinic (m)phase represented by Formula 2 as an active site. These are referred toas “m-LaV₃O₉”.

According to embodiments of the present invention, the active sitessubstantially consists of lanthanum vanadates. For example, lanthanumvanadates may be included in the active site in an amount of 90 wt % ormore. Preferably, the active site may include 95 wt % or more, morepreferably 99 wt % or more, of lanthanum vanadates and the remainder mayconsist of inevitable materials that may be generated during themanufacturing process. Unlike a conventional SCR catalyst includinglanthanum as a promotor for enhancing thermal stability at hightemperature and improving performance at both low and high temperature,the catalyst according to an embodiment of the present invention mayhave a surface with high NO_(X) conversion and high N₂ selectivityduring SCR by applying a lanthanum vanadate as an active site.

In addition, since the catalyst according to embodiments of the presentinvention includes a composite oxide of vanadium and lanthanum as anactive site, superior catalytic properties may be obtained when comparedto catalysts including a vanadium oxide and a lanthanum oxideseparately. The catalyst according to an embodiment of the presentinvention may have minimized poisoning by SO₂ and excellent resistanceto poisons (H₂O/SO₂/AS/ABS) when compared with conventional SCRcatalysts for removing nitrogen oxides including only a vanadium oxideas an active site.

The catalyst for NO_(X) reduction according to the third embodiment ofthe present invention has a configuration in which both the first activesite and the second active site are supported on one support. The firstactive site and the second active site may be randomly distributed onthe support, and a relative weight ratio of the first active site to thesecond active site may vary in the range of 0.1:99.9 to 99.9:0.1.

The above-described vanadates according to an embodiment of the presentinvention may be manufactured by various methods. For example, thevanadates may be manufactured by at least one method of hydrothermalsynthesis, solvothermal synthesis, a mechano-chemical method such asball-milling, non-templated or templated synthesis, a wet or dryimpregnation method, and a thermal decomposition method using a Mn-V,Co-V, or Ni-V based complex.

The vanadate may be distributed on a porous support which will bedescribed below and have a diameter (maximum diameter) of 0.1 nm to 500μm. In this regard, the vanadates may be in an amount of 10⁻⁴ parts byweight to 50 parts by weight based on 100 parts by weight of thesupport.

The above-described catalyst for NO_(X) reduction according to anembodiment of the present invention may further include a promotor. Theactive sites of the catalyst for NO_(X) reduction need to inhibitadsorption of sulfur dioxide (SO₂) included in flue gas or have lowperformance in oxidation of sulfur dioxide (SO₂). Ammonia (NH₃) used asa reducing agent reacts with sulfur trioxide (SO₃) as shown in ReactionSchemes (4) to (6) below to precipitate poisoning substances such asammonium sulfate or ammonium bisulfate on the surface of the catalyst.Ammonium sulfate may be irreversibly adsorbed to the active site of thecatalyst at a low temperature of 300° C. or lower. Ammonium sulfateadsorbed to the surface of the catalyst inhibits adsorption of nitrogenoxides (NO_(X)) and ammonia, as the reducing agent, and thus SCRactivity of the catalyst per unit hour may decrease. In addition, sulfurtrioxide (SO₃) generated by oxidation of sulfur dioxide binds to watervapor included in flue gas to produce sulfuric acid (H₂SO₄), which maycause a problem of corrosion at a downstream system of the SCR process.SO₂+½O₂→SO₃  (4)SO₃+2NH₃+H₂O →(NH₄)₂SO₄  (5)SO₃+NH₃+H₂O→(NH₄)HSO₄  (6)

The promotor may play a role in improving resistance to poisoning by apoisoning substance such as sulfur dioxide (SO₂) or ammonium sulfatesoccurring during SCR reaction on the surface of the catalyst. Forexample, the promotor may reduce a binding energy between the sulfurdioxide (SO₂) and the surface of the catalyst. Accordingly, oxidation ofsulfur dioxide (SO₂) (Reaction Scheme 4) that may occur during SCRreaction at a low temperature may be minimized. In addition, the amountof ammonium sulfate (AS, Reaction Scheme 5) or ammonium bisulfate (ABS,Reaction Scheme 6) generated by reaction between sulfur dioxide andammonia and adsorbed to the surface of the catalyst may be minimized,thereby preventing a decrease in SCR activity of the catalyst per unithour caused by poisoning of the surface of the catalyst. In addition,the promotor may be added as a component constituting the surface of thecatalyst capable of decomposing the above-described AS and ABS at a lowtemperature.

The promotor includes a Group 15 or 16 element. The Group 15 or 16element may include at least one element selected from the groupconsisting of nitrogen (N), phosphorus (P), sulfur (5), arsenic (As),selenium (Se), antimony (Sb), tellurium (Te), bismuth (Bi), polonium(Po), moscovium (Mc), and livermorium (Lv), or any combination thereof.The amount of the promotor may be from 10⁻⁴ parts by weight to 50 partsby weight, preferably 3 parts by weight or less, and more preferably 0.5to 2 parts by weight, based on 100 parts by weight of the support.

The support plays a role in distributing and supporting the lanthanumvanadate and the promotor. The active site of the catalyst needs to havehigh oxidizing and reducing properties for easy adsorption andconversion of nitrogen oxides (NO_(X)). In this case, when the catalystis manufactured by supporting the vanadate on an appropriate support,highly reactive oxygen species (O₂) present in the support may beefficiently supplied to the active site. That is, oxidizing and reducingproperties of the catalyst may be improved. At the same time, when thevanadate is distributed on the support with a high density, thecatalytic efficiency may further be increased. Therefore, a catalyst forNO_(X) reduction including the support capable of providing theabove-described environment may be manufactured.

The support may include carbon (C) or a metal oxide. The metal oxide maybe selected from Al₂O₃, MgO, ZrO₂, CeO₂, TiO₂, and SiO₂.

The catalyst for NO_(X) reduction according to an embodiment of thepresent invention may have a morphology with a large surface area. Asthe surface area increases, adsorption rates of reactants, i.e.,nitrogen oxides or ammonia, increase, and reaction rates increase,thereby increasing reduction efficiency of nitrogen oxides (NO_(X)). Inorder to obtain a wide surface area, the catalyst may have a porousstructure. For example, a porous structure having a wide surface areamay be configured by aggregating a powder material used to form thesupport by calcining.

The catalyst for NO_(X) reduction according to an embodiment of thepresent invention may be functionalized by sulfating the surfacethereof. The sulfation according to the present invention refers tofunctionalization of the catalyst with SO_(Y) ²⁻. As used herein, theterm “functionalization” may indicate a process of improving performanceof the catalyst by increasing the number of active sites of the catalystor by improving characteristics such as adsorption of a reactant to thecatalyst. For example, when the catalyst for NO_(X) reduction of thepresent invention is sulfated and functionalized with SO_(Y) ²⁻, thesurface of the catalyst advantageous for adsorption and convention ofnitrogen oxides may be implemented and new active sites may be formed.

The properties of S—O bonds included in the SO_(Y) ²⁻ species bonded tometal species on the surface of the catalyst may be adjusted byfunctionalization with SO_(Y) ²⁻ by sulfating the surface of thecatalyst. Specifically, SO_(Y) ²⁻ species present on the surface of thecatalyst may bind to the metal species of the catalyst in a bi-dentatebinding form, when they have ionic character, and bind to the metalspecies in a mono-dentate binding, when they have covalent character.SCR reaction performance of the catalyst may vary according todistribution in the catalyst in the bonded form described above.

In this case, according to an embodiment of the present invention,sulfation may be performed by a reaction gas including SO₂ and O₂. Inaddition, SO₂ and O₂ included in the reaction gas may have aconcentration of 10 ppm to 10⁵ ppm, a flow rate of 10⁻⁵ mL min⁻¹ to 10⁵mL min⁻¹, a pressure of 10⁻⁵ bar to 10⁵ bar. In addition, the sulfationmay be performed at a temperature of 200° C. to 800° C. for 0.1 hours to24 hours.

When the conditions for sulfation of the catalyst are less than theabove ranges, functionalization effects of SO_(Y) ²⁻ on the catalyst maybe insufficient. Also, when the conditions are greater than the aboveranges, oxygen species (O_(α)), which improve oxidation and reductioncharacteristics of the surface of the catalyst during SCR reaction orimprove NO₂ production efficiency for fast SCR reaction of Equation (3)below, may disappear due to excessive functionalization of the surfaceof the support. Therefore, sulfation of the catalyst may be performedwithin the above ranges of conditions.NO+NO₂+2NH₃→2N₂+3H₂O  (3)

The catalyst modified by SO_(Y) ²⁻ functionalization by sulfationincludes SO_(Y) ²⁻—NH₄ species additionally formed thereon. SO_(Y)²⁻—NH₄ species serve as Brönsted acid sites to which the reducing agent,ammonia (NH₃), is adsorbed. That is, the catalyst functionalized bysulfation according to the present invention may have an increasednumber of reaction active sites compared to non-functionalizedcatalysts. In addition, the catalyst modified by functionalization usingSO_(Y) ²⁻ may include additionally formed metal-SO_(Y) ²⁻ species,thereby having improved oxidation/reduction characteristics whencompared to non-functionalized catalysts. In addition, the metal-SO_(Y)²⁻ species may increase NO₂ generation efficiency for fast SCR reactionshown in Reaction Scheme (3) above.

That is, in accordance with SO_(Y) ²⁻ (where Y is 3 or 4)functionalization (sulfation) conditions, the number of acid sites maybe adjusted or binding strength with reactants (NO_(X) andNH₃)/poisoning substances (AS and ABS) may be adjusted. Therefore, whena vanadate optimal for SCR reaction is synthesized, (1) a plurality ofBrönsted acid sites may be provided, (2) Lewis acid sites unsaturateddue to a plurality of coordinate bonds may be provided, (3) optimumreaction intensity with reactants appropriate for efficient progress ofturnover cycles of NO_(X) may be provided, (4) NO oxidation efficiencyappropriate for fast SCR reaction may be provided, and (5) the vanadatemay be a component of a catalyst surface having the ability to decomposepoisoning substances of AS and ABS at a low temperature, during SCRreaction.

Hereinafter, a method of manufacturing a catalyst for NO_(X) reductionaccording to an embodiment of the present invention will be described.

First, a vanadium precursor solution and a lanthanum precursor solutionare prepared and mixed to prepare a mixed solution. After sufficientlystirring the mixed solution, the mixed solution is subjected tohydrothermal synthesis or dehydration to obtain solids, and the solidsare calcined to prepare a catalyst for NO_(X) reduction in which alanthanum vanadate is distributed.

In this regard, LaVO₄ active sites having different crystal phases(tetragonal or monoclinic) may be distributed on the support bydiversifying types of compounds capable of forming coordinate bonds withvanadium ions (V⁵⁺) (oxalic acid or ethylenediaminetetraacetic acid).Also, by adjusting the pH of the mixed solution, catalysts in which bothLaVO₄ active sites and LaV₃O₉ active sites are distributed on thesupport or only LaV₃O₉ active sites are distributed on the support maybe manufactured.

The vanadium precursor solution may be, for example, a solution in whicha vanadium compound is dissolved in a solvent. Examples of the vanadiumcompound include NH₄VO₃, NaVO₃, VCl₂, VCl₃, VBr₃, VCl₃⋅3C₄H₈O,VO(C₅H₇O₂)₂, VO(OC₂H₅)₃, VC₁₀H₁₀Cl₂, VC₁₈H₁₄l, VOCl₃, VOF₃,VO(OCH(CH₃)₂)₃, V(C₅H₇O₂)₃, VOSO₄ and V(C₅H₅)₂.

The lanthanum precursor solution may be, for example, a solution inwhich a lanthanum compound is dissolved in a solvent. Examples of thelanthanum compound include LaF₃, LaB₆, LaCl₃, La(CH₃CO₂)₃, Lal₃,La₂(C₂O₄)₃, La(CF₃SO₃)₃, La(NO₃)₃, La(C₉H₂₁O₃), La(C₅H₇O₂)₃, LaBr₃,LaPO₄, La₂(CO₃)₃, La(OH)₃, and La₂(SO₄)₃.

In the above-described manufacturing method, a promotor may be formed inthe catalyst by using a support to which a Group 15 or 16 element isadded. For example, powder of a substance constituting the support ismixed with a solution in which a compound of a Group 15 or 16 element isdissolved, stirred, and dehydrated, and then calcined to prepare asupport mixed with a promotor.

After manufacturing the catalyst, SO_(Y) ²⁻ functionalization forimproving catalytic properties may further be performed. SO_(Y) ²⁻functionalization may be performed by exposing the surface of thecatalyst to a processing gas including sulfur dioxide (SO₂) and oxygen(O₂) by flowing the processing gas under predetermined flow rate andpressure onto the surface of the catalyst. In Table 1 below, conditionsfor SO_(Y) ²⁻ functionalization are shown.

TABLE 1 SO₂ Oxygen Flow rate of Exposure Processing content contentPressure processing gas time temperature (ppm) (vol %) (bar) (mL min⁻¹)(h) (° C.) 10~10⁵ 10⁻⁵~90 10⁻⁵~10⁵ 10⁻⁵~10⁵ 0.1~24 200~800

When the conditions for SO_(Y) ²⁻ functionalization include atemperature lower than 200° C., an exposure time shorter than 0.1 hours,a SO₂ content less than 10 ppm, an oxygen (O₂) content less than 10⁻⁵vol %, a flow rate slower than 10⁻⁵ mL min⁻¹, or a pressure lower than10⁻⁵ bar, SO_(Y) ²⁻ functionalization effects on the surface of thecatalyst may be insignificant. On the contrary, when the conditionsinclude a temperature higher than 800° C., an exposure time longer than24 hours, a SO₂ content more than 10⁵ ppm, an oxygen (O₂) content morethan 90 vol %, a flow rate faster than 10⁵ mL min⁻¹, or a pressurehigher than 10⁵ bar, the surface of the support is excessivelyfunctionalized with SO_(Y) ²⁻, resulting in disappearance of oxygen(O_(n)) species that increase activity of SCR reaction. Therefore,SO_(Y) ²⁻ functionalization on the surface of the catalyst may beperformed under the conditions within the above-described ranges.

Hereinafter, the present invention will be described in more detail withreference to the following examples. However, the following experimentalexamples are merely presented to exemplify the present invention, andthe scope of the present invention is not limited thereto.

Example 1 Preparation of t-LaVO₄ Catalyst

0.79 mmol of ethylenediaminetetraacetic acid (EDTA) was added to asolution prepared by dissolving 0.79 mmol of NH₄VO₃ in 48 mL ofdistilled water, and 0.79 mmol of La(NO₃)₃·6H₂O was added thereto andstirred. Subsequently, 1.85 g of anatase TiO₂ powder (support) was addedto the mixed solution, and the mixed solution was stirred for 2 hourswhile maintaining a pH of 4. After the prepared mixed solution wasexposed to hydrothermal synthesis conditions at 180° C. for 48 hours,the resultant was cooled, filtered at room temperature, washed withwater, and dried. The dried synthetic intermediate substance wascalcined at 500° C. for 5 hours. Solids obtained after calcination wereplaced in a reactor and exposed to sulfur dioxide (SO₂) and oxygen (O₂),both diluted with N₂, by simultaneously flowing SO₂ and O₂ thereinto ata flow rate of 500 mL min⁻¹ at ambient atmospheric pressure at 500° C.for 45 minutes, and then cooled to room temperature under N₂ atmosphere.In the exposure process, the SO₂ content was 500 ppm and the O₂ contentwas 3 vol %. Under the conditions as described above, a catalystaccording to Example 1 functionalized with SO_(Y) ²⁻ (where Y is 3 or 4)was prepared. Hereinafter, the catalyst of Example 1 is referred to ast-LaVO₄.

Example 2 l Preparation of m-LaVO₄ Catalyst

A catalyst according to Example 2 in which only m-LaVO₄ was distributedon the surface of the TiO₂ support was prepared under the sameconditions as the synthesis conditions used in the preparation of thet-LaVO₄ catalyst of Example 1, except that 0.79 mmol of oxalic acid wasused instead of 0.79 mmol of EDTA. Hereinafter, the catalyst of Example2 is referred to as m-LaVO₄.

Example 3 Preparation of m-LaVa₄/m-LaV₃O₉ Catalyst

A catalyst according to Example 3 in which both m-LaVO₄ and m-LaV₃O₉were distributed on the surface of the TiO₂ support was prepared underthe same conditions as the synthesis conditions used in the preparationof the m-La VO₄ catalyst of Example 2, except that the pH was adjustedto 2 instead of 4. Hereinafter, the catalyst of Example 3 is referred toas m-LaVO₄/m-LaV₃O₉.

Example 4 Preparation of m-LaV₃O₉ Catalyst

A catalyst according to Example 4 in which only m-LaV₃O₉ was distributedon the surface of the TiO₂ support was prepared under the sameconditions as the synthesis conditions used in the preparation of them-La VO₄ catalyst of Example 2, except that the pH was adjusted to 1instead of 4. Hereinafter, the catalyst of Example 4 is referred to asm-LaV₃O₉.

Example 5 Preparation of m-LaV₃O₉—Sb Catalyst

A catalyst according to Example 5 was prepared under the same conditionsas the synthesis conditions used in the preparation of the m-LaV₃O₉catalyst of Example 4, except that 1.85 g of TiO₂ powder including anantimony oxide (Sb oxide) as a promotor. Hereinafter, the catalystaccording to Example 5 is referred to as m-LaV₃O₉—Sb. In synthesis ofTiO₂ powder (support) including the Sb oxide as a promotor, 19.4 g ofTiO₂ was added to 200 ml of distilled water to prepare an aqueoussolution and a solution prepared by dissolving 1.47 g of Sb(CH₃COOH)₃ in50 ml of acetic acid was added to the aqueous solution, and then themixture was stirred, dehydrated, and calcined at 500° C. for 5 hours toprepare TiO powder including 3 wt % of Sb relative to TiO₂.

Comparative Example 1 Preparation of t-ErVO₄ Catalyst

A catalyst according to Comparative Example 1 having a similar vanadium(V) content (2 wt % or less) to those of the catalysts according toExample 1 to 5 and including ErVO₄ having a tetragonal crystal phase asan active site was prepared. Specifically, a solution prepared bydissolving 3.93 mmol of Er(NO₃)₃·5H₂O in 70 mL of distilled water wasadded to a solution prepared by dissolving 3.93 mmol of NH₄VO₃ in 170 mLof distilled water to prepare a mixed solution, and the mixed solutionwas stirred for 1 hour. 9.14 g of TiO₂ powder was added to the mixedsolution and stirred for 1 hour, and then the pH was adjusted to 8(suitable for nucleation and growth of tetragonal ErVO₄), stirred for 4hours, and dehydrated. Solids obtained therefrom were calcined at 500°C. for 5 hours. The solids obtained after calcination were placed in areactor and exposed to sulfur dioxide (SO₂) and oxygen (O₂), bothdiluted with N₂, by simultaneously flowing SO₂ and O₂ thereinto at aflow rate of 500 mL min⁻¹ at ambient atmospheric pressure at 500° C. for45 minutes, and then cooled to room temperature under N₂ atmosphere. Inthe exposure process, the SO₂ content was 500 ppm and the O₂ content was3 vol %. Under the conditions as described above, a catalyst accordingto Comparative Example 1 functionalized with SO_(Y) ²⁻ (where Y is 3 or4) was prepared. Hereinafter, the catalyst of Comparative Example 1 isreferred to as t-ErVO₄.

Comparative Example 2 Preparation of t-Ce_(0.5)Er_(0.5)VO₄ Catalyst

A catalyst according to Comparative Example 2 having a similar vanadium(V) content (2 wt % or less) to those of the catalysts according toExample 1 to 5 and including Ce_(0.5)Er_(0.5)VO₄ having a tetragonalcrystal phase as an active site was prepared. Specifically, a solutionprepared by dissolving 1.96 mmol of Ce(NO₃)₃·6H₂O and 1.96 mmol ofEr(NO₃)₃·5H₂O in 70 mL of distilled water was added to a solutionprepared by dissolving 3.93 mmol of NH₄VO₃ in 170 mL of distilled waterto prepare a mixed solution, and the mixed solution was stirred for 1hour. 9.19 g of TiO₂ powder was added to the mixed solution and stirredfor 1 hour, and then the pH was adjusted to 8 (suitable for nucleationand growth of tetragonal Ce_(0.5)Er_(0.5)VO₄), stirred for 4 hours, anddehydrated. Solids obtained therefrom were calcined at 500° C. for 5hours. The solids obtained after calcination were placed in a reactorand exposed to sulfur dioxide (SO₂) and oxygen (O₂), both diluted withN₂, by simultaneously flowing SO₂ and O₂ thereinto at a flow rate of 500mL min⁻¹ at ambient atmospheric pressure at 500° C. for 45 minutes, andthen cooled to room temperature under N₂ atmosphere. In the exposureprocess, the SO₂ content was 500 ppm and the O₂ content was 3 vol %.Under the conditions as described above, a catalyst according toComparative Example 2 functionalized with SO_(Y) ²⁻ (where Y is 3 or 4)was prepared. Hereinafter, the catalyst of Comparative Example 1 isreferred to as t-Ce_(0.5)Er_(0.5)VO₄ catalyst.

Comparative Example 3 Preparation of V₂—W₅ Catalyst

A catalyst according to Comparative Example 3 having a similar vanadium(V) content (2 wt % or less) to those of the catalysts according toExample 1 to 5 and including tungsten as an active site was prepared.Specifically, 9.3 g of anatase TiO₂ powder was added to a solutionprepared by dissolving 0.46 g of NH₄VO₃, 0.67 g of(NH₄)₁₀(H₂W₁₂O₄₂)·4H₂O, and 0.84 g of C₂H₂O₄·2H₂O in 100 mL of distilledwater, and the mixed solution was stirred and dehydrated. Then, theresultant was continuously subjected to calcination at 500° C. for 5hours to prepare a catalyst including tungsten W. In the catalystaccording to Comparative Example 3, vanadium oxide and tungsten oxide,which are independently present, are physically mixed as active sites.The prepared catalyst was exposed to the conditions for SO_(Y) ²⁻ (whereY is 3 or 4) functionalization according to Example 1, thereby finallypreparing the catalyst of Comparative Example 3. Hereinafter, thecatalyst of Comparative Example 3 will be referred to as V₂—W₅ catalystfor descriptive convenience.

Examples 6 and 7 and Comparative Example 4 Preparation of m-LaV₃O₉—Na,m-LaV₃O₉—Sb—Na, and V₂—W₅—Na Catalysts

The surface of the m-LaV₃O₉—Sb catalyst prepared in Example 5 wasintentionally poisoned by introducing Na species onto the surface of thecatalyst in an amount of 60 mol % based on a total number moles of La,V, and Sb included in the m-LaV₃O₉—Sb catalyst, thereby preparingm-LaV₃O₉—Sb—Na. Specifically, solids obtained by mechanically mixing0.08268 g of NaNO₃ with 1.6 g of Mn—Se (S) catalyst were calcined at500° C. for 5 hours to prepare m-LaV₃O₉—Sb—Na catalyst according toExample 7. The surfaces of the m-LaV₃O₉ and V₂—W₅ catalysts preparedaccording to Example 4 and Comparative Example 3 respectively werepoisoned under the same conditions as described above to preparem-LaV₃O₉—Na and V₂—W₅—Na catalysts according to Example 6 andComparative Example 4 respectively.

Examples 8 and 9 and Comparative Example 5 Preparation of m-LaV₃O₉—HT,m-LaV₃O₉—Sb—HT, and V₂—W₅—HT Catalysts

The m-LaV₃O₉, m-LaV₃O₉—Sb and V₂—W₅ catalysts prepared in Examples 4 and5 and Comparative Example 3 were placed in a reactor and exposed tooxygen (O₂) diluted with N₂ by flowing O₂ and water vapor (H₂O)thereinto at a flow rate of 500 mL min⁻¹ at ambient atmospheric pressureat 700° C. for 10 hours, and then cooled to room temperature under N₂atmosphere. In the exposure process, the O₂ content was 3 vol % and thewater vapor (H₂O) content was 6 vol %. Under the conditions as describedabove, catalysts exposed to hydrothermal aging according to Examples 8and 9 and Comparative Example 5 were prepared. Hereinafter, thecatalysts of Examples 8 and 9 and Comparative Example 5 are referred toas m-LaV₃O₉—HT, m-LaV₃O₉—Sb—HT and V₂—W₅—HT, respectively.

Experimental Example 1 Analysis of Characteristics of Catalysts

Surface morphologies of the catalysts prepared in Examples 1 to 5 wereanalyzed by scanning electron microscopy (SEM) and high resolutiontransmission electron microscopy (HRTEM) and the results are shown inFIGS. 1 and 2 , respectively.

Referring to FIGS. 1 and 2 , it was confirmed that the preparedcatalysts included porous supports formed of TiO₂ agglomerates having aparticle size (maximum diameter) of several hundred nanometers toseveral hundred micrometers.

In order to evaluate the degree of porosity of the catalysts of Examples1 to 5, BET surface areas and BJH pore volumes were measured byconducting N₂ physisorption experiment. In addition, components of thecatalysts prepared in Examples 1 to 5 were analyzed using X-rayfluorescence (XRF). Measurement results are shown in Table 2.

TABLE 2 BET surface BJH pore V content La:V S content area volume (wt.%) (molar ratio) (wt. %) Example 1 70 m² g⁻¹ 0.3 cm³ g⁻¹ 1.9 (±0.1), 1.0(±0.1):1 1.0 (±0.1) Example 2 73 m² g⁻¹ 0.3 cm³ g⁻¹ 2.0 (±0.3), 1.0(±0.3):1 1.0 (±0.1) Example 3 66 m² g⁻¹ 0.2 cm³ g⁻¹ 2.0 (±0.1), 0.6(±0.1):1 0.8 (±0.1) Example 4 60 m² g⁻¹ 0.2 cm³ g⁻¹ 2.0 (±0.1), 0.3(±0.1):1 0.6 (±0.1) Example 5 80 m² g⁻¹ 0.3 cm³ g⁻¹ 2.0 (±0.2), 0.3(±0.1):1 0.6 (±0.1)

Based on the BET surface areas and BJH pore volumes, it was confirmedthat the catalysts of Examples 1 to 5 had porous structures. Inaddition, the catalysts had the same V content of 2 wt % based on thetotal weight of the catalysts.

It was confirmed that the molar ratios of La:V of the catalysts ofExamples 1 to 5 were similar to theoretical molar ratios (1:1 inExamples 1 and 2; 0.33:1 to 1:1 in Example 3; and 0.33:1 in Examples 4and 5). Thus, it was confirmed that LaVO₄ or LaV₃O₉ were successfullydistributed on the porous TiO₂ support on the surface of the catalystsof Examples 1 to 5.

Crystal structures of the catalysts of Examples 1 to 5 were analyzed byusing an X-ray diffractometer, and X-ray diffraction (XRD) patternsobtained therefrom are shown in FIG. 3 .

Referring to FIG. 3 , anatase phase crystal planes having a tetragonalcrystal structure indicating the TiO₂ support were observed in all ofthe catalysts of Examples 1 to 5. Meanwhile, crystal planes indicatingtetragonal (t-) LaVO₄ or monoclinic (m-) LaVO₄ crystal particles wereobserved in the XRD patterns of Examples 1 and 2, respectively. Inaddition, crystal planes indicating monoclinic (m-) LaVO₄ and monoclinic(m-) LaV₃O₉ crystal particles were simultaneously observed in the XRDpattern of Example 3. On the contrary, the crystal plane indicating themonoclinic (m-) LaVO₄ and monoclinic (m-) LaV₃O₉ crystal particles werenot observed in the XRD patterns of Examples 4 and 5. This is understoodbecause the size or amount of vanadate crystal particles distributed onthe support are not sufficient for X-ray diffraction. Thus, thecatalysts of Examples 1 to 5 were analyzed using selected area electrondiffraction (SAED) patterns and the results are shown in FIG. 4 .

Referring to FIG. 4 , (101), (211), (220), and (103) crystal planes oftetragonal (t-) LaVO₄ were observed in the catalyst of Example 1.(−101), (101), and (−112) crystal planes of the monoclinic (m-) LaVO₄were observed in the catalyst of Example 2. In addition, (−111), (001),(−112) crystal planes of monoclinic (m-) LaVO₄ and (−101) crystal planeof monoclinic (m-) LaV₃O₉ were observed simultaneously in the catalystof Example 3. Importantly, (001), (−111), (−112) or (011), and (−212)crystal planes of monoclinic (m-) LaV₃O₉ were observed in Examples 4 and5.

Also, (101) and (103) crystal planes corresponding to the anatase phaseof TiO₂ having the tetragonal crystal structure indicating the TiO₂support were observed in all of the catalysts of Examples 1 to 5. Theseresults are identical to the analysis results of XRD patterns of FIG. 3.

As shown in FIG. 4 , patterns of materials other than lanthanumvanadate, e.g., a vanadium oxide or a lanthanum oxide, were not observedin Examples 1 to 5. That is, in Examples 1 to 5 according to the presentinvention, the vanadium oxide, vanadium, and the lanthanum oxideconstitute one composite oxide (lanthanum vanadate), which is not asimple mixture of independent the vanadium oxide and the lanthanumoxide.

Hereinafter, results of SCR performance analysis of the catalysts ofExamples 1 to 9 according to the present invention and ComparativeExamples 1 to 5 will be described with reference to FIGS. 5 to 10 .

Experimental Example 2 Performance Analysis of SCR Reaction (1)

Performance of the SCR process was measured using the catalysts ofExamples 1 to 5. NO_(X) conversion (X_(Nox)) is shown in FIG. 5 wheninjecting H₂O or O₂ at 220° C. As the conditions of the SCR process, areaction fluid included 800 ppm of NO_(X), 800 ppm of NH₃, 3 vol % ofO₂, 6 vol % of H₂O and inert gas of N₂, a total flow rate was 500mLmin⁻¹, and a space velocity was 30,000 hr⁻¹.

Referring to FIG. 5 , it was confirmed that X_(NOX) values decreased inall cases of Examples 1 to 5 in the presence of water vapor (H₂O) thatinhibits adsorption of NH₃ during SCR reaction. However, it wasconfirmed that the X_(NOX) values of the catalysts of Examples 3 to 5were less decreased than those of the catalysts of Examples 1 and 2,indicating that the catalysts of Examples 3 to 5 had superior resistanceto H₂O to that of the catalysts of Examples 1 and 2. In addition, FIG. 5shows a decreasing tendency of X_(NOX) values of the catalysts in thepresence of H₂O under the conditions in which the supply of O₂ is shutoff. Specifically, the degrees of X_(NOX) value decreases of thecatalysts of Examples 3 to 5 were relatively small compared to those ofthe catalysts of Examples 1 and 2. This indicates that the catalysts ofExamples 3 to 5 had excellent redox cycling character during SCRreaction when compared with the catalysts of Examples 1 and 2. Inaddition, N₂ selectivity (S_(N2)) of the catalysts was almost 100% overthe entire experimental section. This indicates that the appropriatemixture of m-LaV₃O₉ or m-LaV₃O₉ and m-LaVO₄ contained on the surfaces orthe Sb oxide as a promotor improved resistance to H₂O and redox cyclingcharacter in SCR reaction in the catalysts of Examples 3 to 5.

Experimental Example 3 Performance Analysis of SCR Reaction (2)

Performance of the SCR process was measured using the catalyst ofExamples 1 to 5 and Comparative Examples 1 and 2 using a reaction fluid800 ppm of NO_(X), 800 ppm of NH₃, 3 vol % of O₂, 6 vol % of H₂O andinert gas of N₂ at a space velocity of 60,000 hr⁻¹ instead of 30,000hr⁻¹. NO_(X) conversion is shown in FIG. 6A and N₂ selectivity is shownin FIG. 6B. Referring to FIGS. 6A and 6B, it was confirmed that thecatalysts of Examples 1 to 5 had desirable activities during thereaction at a temperature of 400° C. or lower, similarly to those ofExperimental Example 2, despite a considerable amount of water vapor(H₂O). For example, N₂ selectivity (S_(N2)) of the catalysts was almost100% at a temperature of 400° C. or lower. It was confirmed that thecatalysts of Examples 3 to 5 showed relatively large X_(NOX) values at atemperature of 400° C. or lower when compared to the catalysts ofExamples 1 and 2. This indicates that the appropriate mixture ofm-LaV₃O₉ or m-LaV₃O₉ and m-LaVO₄ contained on the surfaces or the Sboxide as a promotor improved SCR reaction performance including watervapor (H₂O) in the catalysts of Examples 3 to 5. In addition, it wasconfirmed that the catalysts of Examples 3 to 5 provides similar orrelatively large X_(NOX) values compared to the catalysts of ComparativeExamples 1 and 2 at a temperature of 400° C. or lower. This indicatesthat the appropriate mixture of m-LaV₃O₉ or m-LaV₃O₉ and m-LaVO₄ or theSb oxide as a promotor suggested herein improved denitrification whencompared to previously reported t-ErVO₄ and t-Ce_(0.5)Er_(0.5)VO₄.

Experimental Example 4 Performance Analysis of SCR Reaction (3)

Performance of the SCR process was measured using the catalyst ofExamples 1 to 5 and Comparative Example 3 under the same reactionconditions as those of Experimental Example 3 in the presence of 500 ppmof SO₂, and NO_(X) conversion is shown in FIG. 7A and N₂ selectivity isshown in FIG. 7B. Referring to FIGS. 7A and 7B, it was confirmed thatthe catalysts of Examples 1 to 5 had desirable activities during thereaction at a temperature of 400° C. or lower, similarly to those ofExperimental Example 3, despite considerable amounts of water vapor(H₂O) and sulfur dioxide (SO₂). For example, N₂ selectivity (S_(N2)) ofthe catalysts was almost 100% at a temperature of 400° C. or lower. Itwas confirmed that the catalysts of Examples 3 to 5 showed relativelylarge X_(NOX) values at a temperature of 400° C. or lower when comparedto the catalysts of Examples 1 and 2, which are similar or increasedX_(NOX) values at a temperature of 400° C. or lower when compared to thecatalyst of Comparative Example 3 commonly used in the art. Thisindicates that the appropriate mixture of m-LaV₃O₉ or m-LaV₃O₉ andm-LaVO₄ contained on the surfaces or the Sb oxide as a promotor minimizepoisoning by SO₂ in the catalysts of Examples 3 to 5. This indicatesthat the catalysts of Examples 3 to 5 may be applied as SCR catalystsfor reducing NO_(X) contained in exhaust gas of power plants, sinteringfurnaces, and ships including a considerably amount of SO₂, therebyreplacing commercially available catalysts.

Experimental Example 5 Performance Analysis of SCR Reaction (4)

Performance of the SCR process was measured using the catalysts poisonedby Na according to Examples 6 and 7 and the catalyst of ComparativeExample 4 under the same reaction conditions as those of ExperimentalExample 4. As results of the experiment, NO_(X) conversion is shown inFIG. 8A and N₂ selectivity is shown in FIG. 8B.

Referring to FIGS. 8A and 8B, it was confirmed that all of the catalystsshowed decreased performance by the poisoning substance Na. However, thecatalysts of Examples 6 and 7 showed (1) similar or greater S_(N2)values and (2) greater X_(NOX) values than the commercially availablecatalyst of Comparative Example 4 at a temperature of 500° C. or lower.This indicates that the m-LaV₃O₉ or the Sb oxide as a promotor containedon the surfaces of the catalysts of Examples 6 and 7 improved resistanceto poisoning by Na. This indicates that the catalysts of Examples 4 and5 may be applied as SCR catalysts for reducing NO_(X) contained inexhaust gas of power plants, sintering furnaces, ships, and cementfactories including a considerable amount of alkali metal, therebyreplacing commercially available catalysts.

Experimental Example 6 Performance Analysis of SCR Reaction (5)

Performance of the SCR process was measured using the catalysts exposedto hydrothermal aging according to Examples 8 and 9 and the catalyst ofComparative Example 5 under the same reaction conditions as those ofExperimental Example 4. As results of the experiment, NO_(X) conversionis shown in FIG. 9A and N₂ selectivity is shown in FIG. 9B.

Referring to FIGS. 9A and 9B, it was confirmed that all of the catalystsshowed decreased performance by the hydrothermal aging. However, thecatalysts of Examples 8 and 9 showed (1) similar or greater S_(N2)values and (2) greater X_(NOX) values than the commercially availablecatalyst of Comparative Example 5 at a temperature of 500° C. or lower.This indicates that the m-LaV₃O₉ or the Sb oxide as a promotor containedon the surfaces of the catalysts of Examples 8 and 9 improved resistanceto hydrothermal aging. This indicates that the catalysts of Examples 4and 5 may be applied as SCR catalysts for reducing NO_(X) contained inexhaust gas of power plants and heavy equipment periodically exposed tohydrothermal aging, thereby replacing commercially available catalysts.

Experimental Example 7 Performance Analysis of SCR Reaction (6)

Performance of the SCR process was measured using the catalysts ofExamples 4 and 5 and Comparative Example 3 at a space velocity of 30,000hr⁻¹ with a reaction fluid including 800 ppm of NO_(X), 800 ppm of NH₃,500 ppm of SO₂, 3 vol % of O₂, 6 vol % of H₂O and inert gas of N₂ at220° C., and the results are shown in FIG. 10 . Specifically, the NO_(X)conversion (X_(NOX)) of each catalyst was divided by NO_(X) conversion(X_(NOX, 0)) of the early stage of the reaction (in the absence of SO₂).In addition, time required for performance decrease to 70%(X_(NOX)/X_(NOX,0)˜0.7) of the initial performance by poisoning on thecatalyst surface with H₂O/SO₂/AS/ABS was measured.

Referring to FIG. 10 , it was confirmed that the catalysts of Example 4(about 20 hours) and Example 5 (about 23 hours) showed improvedresistance to poisoning substances when compared to the catalyst ofComparative Example 3 (about 13 hours). This indicates that m-LaV₃O₀ orthe Sb oxide as a promotor contained on the surface of the catalysts ofExamples 4 and 5 provide excellent resistance to the poisoningsubstances (H₂O/SO₂/AS/ABS). This indicates that the catalysts ofExamples 4 and 5 may be applied as SCR catalysts for reducing NO_(X)contained in exhaust gas of power plants, sintering furnaces, ships, andcement factories including considerably amounts of SO₂ and H₂O, therebyreplacing commercially available catalysts.

According to embodiments of the present invention to solve the aboveproblems, a catalyst including at least one of the three types oflanthanum vanadates (tetragonal LaVO₄, monoclinic LaVO₄, or monoclinicLaV₃O₉), which is a composite oxide based on chemical bonds betweenlanthanum (La) and vanadium (V), as an active site may be manufactured,and thus the surface of the catalyst may have high NO_(X) conversion andhigh N₂ selectivity during SCR reaction. Also, by applying an oxide of aGroup 15 or 16 element as a promotor or functionalizing (sulfating) thesurface of the catalyst with SO_(Y) ²⁻ (where Y is 3 or 4), (1)desirable interaction between the surface of the active site and NO_(X),NH₃ and H₂O may be induced, (2) redox cycling character may be improved,and (3) durability against poisoning (SO₂, AS, ABS and alkali-metal) orhydrothermal aging that may occur during the SCR reaction may beimproved. Based on these advantages, performance and lifespan ofheterogeneous catalysts for SCR may be significantly improved. However,these problems are exemplary and the scope of the present invention isnot limited thereby.

While one or more embodiments of the present invention have beendescribed with reference to the drawings, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope of thepresent invention as defined by the following claims.

What is claimed is:
 1. A catalyst for reduction of nitrogen oxidescomprising: an active site including lanthanum vanadate represented byat least one of Formula 1 and Formula 2; and a support carrying theactive site; wherein Formula 1 is LaVO₄ wherein LaVO₄ is polymorphousand has a tetragonal or monoclinic crystal structure; and whereinFormula 2 is LaV₃O₉ wherein LaV₃O₉ has a monoclinic crystal structure;and wherein at least one portion of the surface of the catalyst issulfated.
 2. The catalyst of claim 1, wherein the support furthercomprises a promoter that is an oxide of a Group 15 or 16 element. 3.The catalyst of claim 2, wherein an amount of the promotor is in therange of 1 wt % to 5 wt % based on an amount of the support.
 4. Thecatalyst of claim 2, wherein the Group 15 or 16 element is one elementselected from the group consisting of nitrogen (N), phosphorus (P),sulfur (S), arsenic (As), selenium (Se), antimony (Sb), tellurium (Te),bismuth (Bi), polonium (Po), moscovium (Mc), and livermorium (Lv), orany combination thereof.
 5. The catalyst of claim 1, wherein the supportfurther comprises one of carbon (C), Al₂O₃, MgO, ZrO₂, CeO₂, TiO₂, andSiO₂.
 6. The catalyst of claim 1, wherein the amount of the lanthanumvanadate represented by Formula 1 or the lanthanum vanadate representedby Formula 2 is in the range of 10⁻⁴ parts by weight to 50 parts byweight based on 100 parts by weight of the support.
 7. The catalyst ofclaim 1, wherein the support has a porous structure.
 8. A method ofmanufacturing a catalyst for reduction of nitrogen oxides, the methodcomprising: mixing a vanadium precursor solution with a lanthanumprecursor solution; adding a material constituting a support to themixed solution; and obtaining solids from the mixed solution, andcalcining the solids to prepare a catalyst including a support carryinga lanthanum vanadate represented by Formula 1 or 2 as an active site orboth a lanthanum vanadate represented by Formula 1 as a first activesite and a lanthanum vanadate represented by Formula 2 as a secondactive site,LaVO₄, wherein LaVO₄, is polymorphous and has a tetragonal or monocliniccrystal structure  Formula 1LaV₃O₉ wherein LaV₃O₉ has a monoclinic crystal structure; and  Formula 2wherein at least one portion of the surface of the catalyst is sulfated.9. The method of claim 8, wherein the vanadium precursuor solutioncomprises a solution in which at least one of NH₄VO₃, NaVO₃, VCl₂, VCl₃,VBr₃, VCl₃·3C₄H₈O, VO(C₅H₇O₂)₂, VO(OC₂H₅)₃, VC₁₀H₁₀Cl₂, VC₁₈H₁₄I, VOCl₃,VOF₃, VO(OCH(CH₃)₂)₃, V(C₅H₇O₂)₃, VOSO₄, and V(C₅H₅)₂ is dissolved. 10.The method of claim 8, wherein the lanthanum precursor solutioncomprises a solution in which at least one of LaF₃, LaB₆, LaCl₃,La(CH₃CO₂)₃, LaI₃, La₂(C₂O₄)₃, La(CF₃SO₃)₃, La(NO₃)₃, La(C₉H₂₁O₃),La(C₅H₇O₂)₃, LaBr₃, LaPO₄, La₂(CO₃)₃, La(OH)₃, and La₂(SO₄)₃ isdissolved.